Focusing device



A. F. JOBKE.

FOCUSING DEVICE.

APPLICATlON FILED SEPT. 16, 1920.

1,404,440. Patented Jan. 24-, 1922.

B "G 5/ r ,7 i s G D A INVENTOPI UNITED STATES PATENT OFFICE.

AUGUST 1. JOB, 0F PI'JI'IJSBURGH PENNSYLVANIA.

rocusme DEVICE.

Application filed Sptember 16, 1920. Serial No. 410,664.

To all whom it may concern:

Be it known that I, AUGUST F. J claim, a citizen of the United States,residing at Pittsbur h, in'the county of Allegheny and Stateof%ennsylvania,have invented a new and useful Focusin' Device, ofwhichthe following is a speci cation.

My invention relates'to a focusing device, the object of which is toautomatically keep a photographic lens, a plane surface corresponding toan object to be projected and a plane surface corresponding to ascreen-or projecting surface in such posltlons relative to one another,that the image produced through the lens" is sharp at any ratio ofmagnification as well'as reduction.

Another object of this invention is, to

make it adjustable to such an extent as to render it applicable not onlyto the use of a single lens of a certain focal length, but to the focallength of any other lens chosen, thus giving it a usefulness highlydesirable in all kinds of reproduction, and facilitating itsmanufacture, since a single model may lengths.

In the common way of reproduction it is very diflicult to get aperfectly sharp image and practically impossible, if a weak light sourceis used, the reproduction is nearly to the same size, or if the negativehappens to be dense. 'In subh cases one "can improve results 'bystopping the lens down, which has the disadvantage of requiring a longerexposure. This device is to overcome these disadvantages, allowing theuse of a full lens opening, thus permitting much faster work. i

' Being of a very simple construction, based on a simple geometricconfiguration, this invention permits an exact adjustment of its severalelements, and therefore perfectly accurate results can be obtainedthrough its application. attain these objects by applying a mechanism,the principal part of which is a straight lever, and I use the'angularposisition of this lever relative to the optical axis of the combinationto establish both conjugate focal distances.

fully disclosed and made understood in the cover along range'ofdifferent focal following description, Where reference is had to thedrawing, in which:

Figure 1. is a configuration intended to explain geometrically therelations existing Between the different parts of my inven- Figure 2 isa diagrammatic view of the focusing device applied to the elements of anoptical" combination. i Since this invention permits a broadapplication. and will find varied uses in the field of opticalprojection, I'shall not descrlbe it in connection with specificapparatus, but refer only to those elements which are necessary toproject an image through a lens.

In explaining the working of this focusmg device I refer to Figure 1, inwhich A E 1s a rectangular triangle and GDC a right angle, the arms ofwhich are arallel to the catheti of the triangle. The ypothenuse AE maybe movable angularly about D as its fulcrum. It can be shown, thatAGzGDzDGzGE, or' A,G:GD=DG:GE,. Ife we select GDzDCzthe focal length ofa lens, the two dimensions AG and CE or A G and CE are'reciprocals toeach other as factors of the focal length; in otherSpecificationofLefterslafent- Patented Jan. 24, 1922. v

words, they are equivalents of extrafocal the hy'pothenuse determinesthe ratioof the corres onding projection. If the angle at A or is 45,then the rojection is of the ratio=1, and assuming t at A be theposition of the projecting surface andE that of the object to beprojected, an angle at 'A smallerthan 45 corresponds to enlargin whilean angle larger than 45 correspon s to reduction; Generallyspeaking, thetangent of the angle at E is the factor of projection for E as theobject.

Figure 2 shows an optical combination as usedby photo-engravers toobtain a reversed negative with a sensitive plat'e'in the normalposition, or a right-faced negative may be obtained in placing'thesensitive plate in a reversed position. This combination consists of aplane surface at A, re'presenting an object to be projected, a lens B,equipped with a prism or reflector R, and

in the ratio of 1 2 and the leverin the posia plane surface Hrepresenting an easel or sensitive medium. The reflector R turns theoptical axis AB through 90. Since the central point of reflection is atR, instead of the optical center B, the conju ate focal distance is BHplus RB (or R and the bracket W is to provide .the second member to haveBEzthe conjugate focal distance.

A straight lever AE, adapted to be mov able angularly about its fulcrumD, which isv located one focal length from a line AB, garallel to theoptical axis, and from a line E, normal thereto, slides in pivotedbearings A and E, which are movable on the lines mentioned. -Any angularmotion of this lever will produce conjugate focal lengths AB and BE, orA B and BE respectively.

In order to vary the arrangement for a different focal length, thefulcrum D is mounted upon a nut, sliding in a slot placed at 45 to thelines AB and BE and adjusted by means of the screw L, which forconvenient, handling hasthe thumbhead M. The equal focal distance ofanypoint D from AB and BE is therefore always maintained. If the projectionfrom A to H is tion of the fulcrum at D is kept parallel to AE, it caneasily be seen, that the ratio of projection must be the same since thetriangle, A BE is similar to ABE. The plane I-I-will be removed'to theposition H since EH is equal to the corresponding major focal distance.

The application of a movable fulcrum as shown is olf greatest commercialimportance, since the exact focal length of a lens may not be given, oronly assumed to be of a certain magnitude. t would be commerciallyimpossible to manufacture a focusing device for every focal length usedin prac tice, since every style of lens has a different focal length,eventually varying little from a similar competing one. In varying theposition of the fulcrum of the lever, it can be adjusted to a greatrange of lenses and a sha a image always be secured.

ile AE is the position of the lever fol a projection of 1:2, which inthis case is magnification, the opposite, i. e., reduction of 2:1 willbe secured with the osition A,E The position of the plane in H, willresult then in the conjugate focal distance BA,=2BE,.

In the description of this arrangement it must be understood, that thelocations of the difierent parts given are ideal ones,

ivin'g the simplest formof combination.

ny changes of positions relative to the center lines of the lens must bemade up by additional members or a change in dimensions of those used,and since the arrangement shown is only one o'f those. possible to use,I declare such variations as being within the scope of my invention.

What I claim and desire to secure by Letters Patent, is:

1. In a focusing device a lens and a reflector adapted to reflect a rayof light through the optical axis at 90, a plane representin an objectto be projected and a plane adapted to receive an image therefromlocated at conjugate focal distances from the optical center of thelens, a straight lever movable-about a fulcrum located one focal lengthof the said lens from two lines parallel to the two branches of theoptical axis and adapted to out both lines at conjugate focal distancesfrom the point of their intersection, and means to move the said twoplanes simultaneously with the points of intersection of the lever andthe said" lines.

2. In a focusing device a lens and a refiector adapted to reflect a rayof light through the optical axis at 90, a plane representing an objectto be projected and a plane adapted to receive an image therefromlocated at conjugate focal distances from the optical center of thelens, a straight lever movable abouta fulcrum located one focal lengthof the said lens from two lines parallel to thetwo branches of theoptical axis, two pivoted bearings sliding on the arms of the said leverand along the said two lines, their centers establishing conj'ugatelfocal distances on the two lines from the point of their intersection,and means to move the said two planes simultaneously with the saidpivoted bearings.

3. In a focusing device a lens and a reflector adapted to reflect a rayof light through the optical axis at 90, a plane representing an objectto be projected and a plane adapted to receive an image therefromlocated at conjugate focal distances from the optical center of thelens, a straight lever movable about a fulcrum located one focal length.of the said lens from two lines parallel .to the two branches of theoptical axis, the fulcrum being adjustable along a line of 45 betweenthe said lines and from the point of their intersection, two pivotedbearings sliding on the arms of the said lever and along the said lines,their centers establishing conjugate focal distances on the said linesfrom the point of their intersection, and means to move the said twoplanes simultaneously with the said two pivoted bearings.

4. In a focusing device a lens and a reflector adapted to reflect a rayof light through the optical axis at 90, a. plane representing an objectto be projected and a plane adapted to recewe an image therefrom locatedat conjugate focal distances from the optical center of the lens, astraight lever movable about a fulcrum located one 189 {focal length ofthe said lens from two lines parallel to the two'branches of the opticalaxis, the fulcrum being adjustable along a line at 45 between the saidlines and from the point of their intersection, two pivoted bearingssliding onthe arms of the said lever and along thesaid lines, theircenters establishing conjugate focal distances on the said lines fromthe point of their intei'section, means to move the said two planes 10 lsimultaneously with the said two pivoted bearings, and means to changethe position of the fulcrum to suit lenses of different focal lengths.

In testimony whereof I afiix my signature. 15

AUGUST F. J OBKE.

